Buggy code:
private requestor ; ProblemReporter problemReporter ; char [ ] source ; char [ ] completionToken ; char [ ] qualifiedCompletionToken ; boolean resolvingImports = false ; boolean insideQualifiedReference = false ; boolean noProposal = true ; IProblem problem = null ; int startPosition ; int actualCompletionPosition ; int endPosition ; int offset ; HashtableOfObject knownPkgs = new HashtableOfObject ( 10 ) ; HashtableOfObject knownTypes = new HashtableOfObject ( 10 ) ; Scanner nameScanner ; static final char [ ] [ ] baseTypes = new char [ ] [ ] { "boolean" . toCharArray ( ) , "byte" . toCharArray ( ) , "char" . toCharArray ( ) , "double" . toCharArray ( ) , "float" . toCharArray ( ) , "int" . toCharArray ( ) , "long" . toCharArray ( ) , "short" . toCharArray ( ) , "void" . toCharArray ( ) } ; static final char [ ] classField = "class" . toCharArray ( ) ; static final char [ ] lengthField = "length" . toCharArray ( ) ; static final char [ ] cloneMethod = "clone" . toCharArray ( ) ; static final char [ ] THIS = "this" . toCharArray ( ) ; static final char [ ] THROWS = "throws" . toCharArray ( ) ; static InvocationSite FakeInvocationSite = new InvocationSite ( ) { public TypeBinding [ ] genericTypeArguments ( ) { } public boolean isSuperAccess ( ) { } public boolean isTypeAccess ( ) { } public void setActualReceiverType ( ReferenceBinding receiverType ) { } public void setDepth ( int depth ) { } public void setFieldIndex ( int depth ) { } public int sourceStart ( ) { } public int sourceEnd ( ) { } } ; public CompletionEngine ( SearchableEnvironment nameEnvironment , CompletionRequestor requestor , Map settings , IJavaProject javaProject ) { } public void acceptClass ( char [ ] packageName , char [ ] className , int modifiers , AccessRestriction accessRestriction ) { } public void acceptInterface ( char [ ] packageName , char [ ] interfaceName , int modifiers , AccessRestriction accessRestriction ) { } public void acceptPackage ( char [ ] packageName ) { } private void complete ( ASTNode astNode , ASTNode astNodeParent , Binding qualifiedBinding , Scope scope ) { } public void complete ( IType type , char [ ] snippet , int position , char [ ] [ ] localVariableTypeNames , char [ ] [ ] localVariableNames , int [ ] localVariableModifiers , boolean isStatic ) { } private Initializer parseSnippeInitializer ( char [ ] snippet , int position , char [ ] [ ] localVariableTypeNames , char [ ] [ ] localVariableNames , int [ ] localVariableModifiers , boolean isStatic ) { } public void complete ( ICompilationUnit sourceUnit , int completionPosition , int pos ) { } private TypeBinding [ ] computeTypes ( Expression [ ] arguments , BlockScope scope ) { } private void findAnonymousType ( ReferenceBinding currentType , TypeBinding [ ] argTypes , Scope scope , InvocationSite invocationSite ) { } private void findClassField ( char [ ] token , TypeBinding receiverType , Scope scope ) { } private void findExplicitConstructors ( char [ ] name , ReferenceBinding currentType , MethodScope scope , InvocationSite invocationSite ) { } private void findConstructors ( ReferenceBinding currentType , TypeBinding [ ] argTypes , Scope scope , InvocationSite invocationSite , boolean forAnonymousType ) { MethodBinding [ ] methods = currentType . availableMethods ( ) ; if ( methods != null ) { int minArgLength = ( argTypes == null ) ? 0 : argTypes . length ; next : for ( int f = methods . length ; ( -- f ) >= 0 ; ) { MethodBinding constructor = methods [ f ] ; if ( constructor . isConstructor ( ) ) { if ( constructor . isSynthetic ( ) ) continue next ; if ( ( this . options . checkVisibility ) && ( ! ( constructor . canBeSeenBy ( invocationSite , scope ) ) ) ) { if ( ( ! forAnonymousType ) || ( ! ( constructor . isProtected ( ) ) ) ) continue next ; } boolean hasRestrictedAccess = false ; TypeBinding [ ] parameters = constructor . parameters ; int paramLength = parameters . length ; if ( minArgLength > paramLength ) continue next ; for ( int a = minArgLength ; ( -- a ) >= 0 ; ) if ( ( argTypes [ a ] ) != null ) if ( ! ( argTypes [ a ] . isCompatibleWith ( constructor . parameters [ a ] ) ) ) continue next ; char [ ] [ ] parameterPackageNames = new char [ paramLength ] [ ] ; char [ ] [ ] parameterTypeNames = new char [ paramLength ] [ ] ; for ( int i = 0 ; i < paramLength ; i ++ ) { TypeBinding type = parameters [ i ] ; parameterPackageNames [ i ] = type . qualifiedPackageName ( ) ; parameterTypeNames [ i ] = type . qualifiedSourceName ( ) ; } char [ ] [ ] parameterNames = findMethodParameterNames ( constructor , parameterTypeNames ) ; char [ ] completion = CharOperation . NO_CHAR ; if ( ( ( ( this . source ) == null ) || ( ( this . source . length ) <= ( this . endPosition ) ) ) || ( ( this . source [ this . endPosition ] ) != ')' ) ) completion = new char [ ] { ')' } ; if ( forAnonymousType ) { int relevance = computeBaseRelevance ( ) ; relevance += computeRelevanceForInterestingProposal ( ) ; relevance += computeRelevanceForRestrictions ( hasRestrictedAccess ) ; this . noProposal = false ; if ( ! ( this . requestor . isIgnored ( CompletionProposal . ANONYMOUS_CLASS_DECLARATION ) ) ) { CompletionProposal proposal = this . createProposal ( CompletionProposal . ANONYMOUS_CLASS_DECLARATION , this . actualCompletionPosition ) ; proposal . setDeclarationSignature ( Engine . getSignature ( currentType ) ) ; proposal . setSignature ( Engine . getSignature ( constructor ) ) ; proposal . setDeclarationPackageName ( currentType . qualifiedPackageName ( ) ) ; proposal . setDeclarationTypeName ( currentType . qualifiedSourceName ( ) ) ; proposal . setParameterPackageNames ( parameterPackageNames ) ; proposal . setParameterTypeNames ( parameterTypeNames ) ; proposal . setCompletion ( completion ) ; proposal . setFlags ( constructor . modifiers ) ; proposal . setReplaceRange ( ( ( this . endPosition ) - ( this . offset ) ) , ( ( this . endPosition ) - ( this . offset ) ) ) ; proposal . setRelevance ( relevance ) ; <START_BUG> if ( parameterNames == null ) <END_BUG>

Fix:
if ( parameterNames != null )